Vehicles having mechanical drive systems typically transmit torque to their drive wheels via gear arrangements, which are commonly known as differentials. A differential typically transfers rotational motion from an input shaft to each of two wheels disposed on both ends of a drive axle. Differentials are typically able to allow two wheels that are connected to a single axle to rotate at different speeds. Conditions requiring such differential motion may occur when the vehicle is turning or when the two wheels are experiencing different traction conditions.
Even though differentials are effective in preventing wheel slipping for vehicles or machines, they are typically absent from vehicles having systems driving each wheel independently from the others, such as, vehicles having electrical or hydrostatic drive systems. Such vehicles typically lack a direct mechanical linkage between drive wheels because each drive wheel is independently powered by a motor that is associated with that wheel.
One method for controlling the slip of drive wheels in a vehicle is disclosed in U.S. Pat. No. 4,521,856 (the '856 patent) by Phelps et al. The '856 patent discloses an anti-spin apparatus for controllably equalizing the power delivered through a differential mechanism to wheels of a vehicle. The apparatus produces a slip signal that is indicative of a difference in rotational velocity between the wheels. A processor receives the slip signal and applies a brake associated with an individual wheel that is found to be slipping.
Although the apparatus of the '856 patent may apply braking to correct slip, this method of controlling traction dissipates energy at the brakes, which increases fuel consumption and may also accelerate wear of the brakes and/or other drive components of the vehicle.